Available from Nu Horizons Electronics is ON Semiconductor's NCP101x range of self-supplied monolithic switchers. The family of switchers can be connected directly to mains voltage (230V) and offers everything needed to build a rugged and low-cost power supply, including soft-start, frequency jittering, short-circuit protection, skip-cycle, a maximum peak current setpoint and a dynamic self-supply (no need for an auxiliary winding). The NCP101x series integrates a fixed-frequency current-mode controller and a 700V MOSFET, reducing the number of external components required. Unlike other monolithic solutions, these switchers are quiet by nature: during nominal load operation, the part switches at one of the available frequencies (65 - 100 - 130 kHz).

When the current setpoint falls below a given value, e.g. the output power demand diminishes, the IC automatically enters the so-called skip-cycle mode and provides excellent efficiency at light loads. Because this occurs at typically one quarter of the maximum peak value, no acoustic noise is generated. As a result, standby power is reduced to the minimum without any acoustic noise. Short-circuit detection takes place when the feedback signal fades away, in either true short-circuit conditions or in broken Optocoupler cases. External disabling is easily done either simply by pulling the feedback pin down or latching it to ground through an inexpensive SCR for complete latched-off. Soft-start and frequency jittering further ease the development of low-cost, robust offline power supplies.

For improved standby performance, the connection of an auxiliary winding stops DSS operation and helps to consume less than 100mW at high line. In this mode, a built-in latched overvoltage protection prevents from lethal voltage runaways to avoid damaging the Optocoupler. The NCP101x range is available in economical 7-pin dual-in-line and 4-pin SOT-223 packages.